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From: Christian Brauner <christian.brauner@ubuntu.com>
To: Stefan Berger <stefanb@linux.ibm.com>
Cc: linux-integrity@vger.kernel.org, zohar@linux.ibm.com,
	serge@hallyn.com, containers@lists.linux.dev,
	dmitry.kasatkin@gmail.com, ebiederm@xmission.com,
	krzysztof.struczynski@huawei.com, roberto.sassu@huawei.com,
	mpeters@redhat.com, lhinds@redhat.com, lsturman@redhat.com,
	puiterwi@redhat.com, jejb@linux.ibm.com, jamjoom@us.ibm.com,
	linux-kernel@vger.kernel.org, paul@paul-moore.com,
	rgb@redhat.com, linux-security-module@vger.kernel.org,
	jmorris@namei.org
Subject: Re: [RFC 20/20] ima: Setup securityfs_ns for IMA namespace
Date: Thu, 2 Dec 2021 14:18:18 +0100	[thread overview]
Message-ID: <20211202131818.ygzsywwfu4rfcbuy@wittgenstein> (raw)
In-Reply-To: <20211130160654.1418231-21-stefanb@linux.ibm.com>

On Tue, Nov 30, 2021 at 11:06:54AM -0500, Stefan Berger wrote:
> Setup securityfs_ns with symlinks, directories, and files for IMA
> namespacing support. The same directory structure that IMA uses on the
> host is also created for the namespacing case.
> 
> Increment the user namespace's refcount_teardown value by '1' once
> securityfs_ns has been successfully setup since the initialization of the
> filesystem causes an additional reference to the user namespace to be
> taken. The early teardown function will delete the file system and release
> the additional reference.
> 
> The securityfs_ns file and directory ownerships cannot be set when the
> filesystem is setup since at this point the user namespace has not been
> configured yet by the user and therefore the ownership mappings are not
> available, yet. Therefore, adjust the file and directory ownerships when
> an inode's function for determining the permissions of a file or directory
> is accessed.
> 
> This filesystem can now be mounted as follows:
> 
> mount -t securityfs_ns /sys/kernel/security/ /sys/kernel/security/
> 
> The following directories, symlinks, and files are then available.
> 
> $ ls -l sys/kernel/security/
> total 0
> lr--r--r--. 1 nobody nobody 0 Nov 27 06:44 ima -> integrity/ima
> drwxr-xr-x. 3 nobody nobody 0 Nov 27 06:44 integrity
> 
> $ ls -l sys/kernel/security/ima/
> total 0
> -r--r-----. 1 root root 0 Nov 27 06:44 ascii_runtime_measurements
> -r--r-----. 1 root root 0 Nov 27 06:44 binary_runtime_measurements
> -rw-------. 1 root root 0 Nov 27 06:44 policy
> -r--r-----. 1 root root 0 Nov 27 06:44 runtime_measurements_count
> -r--r-----. 1 root root 0 Nov 27 06:44 violations
> 
> Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
> ---
>  include/linux/ima.h                      |  17 +++
>  security/integrity/ima/ima.h             |   2 +
>  security/integrity/ima/ima_fs.c          | 178 ++++++++++++++++++++++-
>  security/integrity/ima/ima_init_ima_ns.c |   6 +-
>  security/integrity/ima/ima_ns.c          |   4 +-
>  5 files changed, 203 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/ima.h b/include/linux/ima.h
> index fe08919df326..a2c5e516f706 100644
> --- a/include/linux/ima.h
> +++ b/include/linux/ima.h
> @@ -221,6 +221,18 @@ struct ima_h_table {
>  	struct hlist_head queue[IMA_MEASURE_HTABLE_SIZE];
>  };
>  
> +enum {
> +	IMAFS_DENTRY_INTEGRITY_DIR = 0,
> +	IMAFS_DENTRY_DIR,
> +	IMAFS_DENTRY_SYMLINK,
> +	IMAFS_DENTRY_BINARY_RUNTIME_MEASUREMENTS,
> +	IMAFS_DENTRY_ASCII_RUNTIME_MEASUREMENTS,
> +	IMAFS_DENTRY_RUNTIME_MEASUREMENTS_COUNT,
> +	IMAFS_DENTRY_VIOLATIONS,
> +	IMAFS_DENTRY_IMA_POLICY,
> +	IMAFS_DENTRY_LAST
> +};
> +
>  struct ima_namespace {
>  	struct kref kref;
>  	struct user_namespace *user_ns;
> @@ -267,6 +279,11 @@ struct ima_namespace {
>  	struct mutex ima_write_mutex;
>  	unsigned long ima_fs_flags;
>  	int valid_policy;
> +
> +	struct dentry *dentry[IMAFS_DENTRY_LAST];
> +	struct vfsmount *mount;
> +	int mount_count;
> +	bool file_ownership_fixes_done;
>  };
>  
>  extern struct ima_namespace init_ima_ns;
> diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
> index bb9763cd5fb1..9bcd71bb716c 100644
> --- a/security/integrity/ima/ima.h
> +++ b/security/integrity/ima/ima.h
> @@ -139,6 +139,8 @@ struct ns_status {
>  /* Internal IMA function definitions */
>  int ima_init(void);
>  int ima_fs_init(void);
> +int ima_fs_ns_init(struct ima_namespace *ns);
> +void ima_fs_ns_free(struct ima_namespace *ns);
>  int ima_add_template_entry(struct ima_namespace *ns,
>  			   struct ima_template_entry *entry, int violation,
>  			   const char *op, struct inode *inode,
> diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
> index 6766bb8262f2..9a14be520268 100644
> --- a/security/integrity/ima/ima_fs.c
> +++ b/security/integrity/ima/ima_fs.c
> @@ -22,6 +22,7 @@
>  #include <linux/parser.h>
>  #include <linux/vmalloc.h>
>  #include <linux/ima.h>
> +#include <linux/namei.h>
>  
>  #include "ima.h"
>  
> @@ -436,8 +437,13 @@ static int ima_release_policy(struct inode *inode, struct file *file)
>  
>  	ima_update_policy(ns);
>  #if !defined(CONFIG_IMA_WRITE_POLICY) && !defined(CONFIG_IMA_READ_POLICY)
> -	securityfs_remove(ima_policy);
> -	ima_policy = NULL;
> +	if (ns == &init_ima_ns) {
> +		securityfs_remove(ima_policy);
> +		ima_policy = NULL;
> +	} else {
> +		securityfs_ns_remove(ns->dentry[IMAFS_DENTRY_POLICY]);
> +		ns->dentry[IMAFS_DENTRY_POLICY] = NULL;
> +	}
>  #elif defined(CONFIG_IMA_WRITE_POLICY)
>  	clear_bit(IMA_FS_BUSY, &ns->ima_fs_flags);
>  #elif defined(CONFIG_IMA_READ_POLICY)
> @@ -509,3 +515,171 @@ int __init ima_fs_init(void)
>  	securityfs_remove(ima_policy);
>  	return -1;
>  }
> +
> +/*
> + * Fix the ownership (uid/gid) of the dentry's that couldn't be set at the
> + * time of their creation because the user namespace wasn't configured, yet.
> + */
> +static void ima_fs_ns_fixup_uid_gid(struct ima_namespace *ns)
> +{
> +	struct inode *inode;
> +	size_t i;
> +
> +	if (ns->file_ownership_fixes_done ||
> +	    ns->user_ns->uid_map.nr_extents == 0)
> +		return;
> +
> +	ns->file_ownership_fixes_done = true;
> +	for (i = 0; i < IMAFS_DENTRY_LAST; i++) {
> +		if (!ns->dentry[i])
> +			continue;
> +		inode = ns->dentry[i]->d_inode;
> +		inode->i_uid = make_kuid(ns->user_ns, 0);
> +		inode->i_gid = make_kgid(ns->user_ns, 0);
> +	}
> +}
> +
> +/* Fix the permissions when a file is opened */
> +int ima_fs_ns_permission(struct user_namespace *mnt_userns, struct inode *inode,
> +			 int mask)
> +{
> +	ima_fs_ns_fixup_uid_gid(get_current_ns());

As noted later in the thread if this is required it means something is
buggy in the current code. That shouldn't be needed.

I think there's a more fundamental issue here. The correct way to do all
this would be to restructure securityfs at least how it works inside of
user namespaces. Currently, securityfs works like debugfs: a single
shared superblock that is pinned by each new inode that is created via:

	simple_pin_fs(&fs_type, &mount, &mount_count);
	simple_release_fs(&mount, &mount_count);

and each mount surfaces the same superblock. Ideally making securityfs
mountable inside of user namespaces should get you a new superblock.
Functions that create files for the ima ns would then be called inside
->fill_super etc.

  parent reply	other threads:[~2021-12-02 13:18 UTC|newest]

Thread overview: 54+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-30 16:06 [RFC 00/20] ima: Namespace IMA with audit support in IMA-ns Stefan Berger
2021-11-30 16:06 ` [RFC 01/20] ima: Add IMA namespace support Stefan Berger
2021-11-30 16:06 ` [RFC 02/20] ima: Define ns_status for storing namespaced iint data Stefan Berger
2021-11-30 16:06 ` [RFC 03/20] ima: Namespace audit status flags Stefan Berger
2021-11-30 16:06 ` [RFC 04/20] ima: Move delayed work queue and variables into ima_namespace Stefan Berger
2021-11-30 16:06 ` [RFC 05/20] ima: Move IMA's keys queue related " Stefan Berger
2021-11-30 16:06 ` [RFC 06/20] ima: Move policy " Stefan Berger
2021-11-30 16:06 ` [RFC 07/20] ima: Move ima_htable " Stefan Berger
2021-11-30 16:06 ` [RFC 08/20] ima: Move measurement list related variables " Stefan Berger
2021-12-02 12:46   ` James Bottomley
2021-12-02 13:41     ` Stefan Berger
2021-12-02 16:29       ` James Bottomley
2021-12-02 16:45         ` Stefan Berger
2021-12-02 17:44           ` James Bottomley
2021-12-02 18:03             ` Stefan Berger
2021-12-02 20:03               ` James Bottomley
2021-11-30 16:06 ` [RFC 09/20] ima: Only accept AUDIT rules for IMA non-init_ima_ns namespaces for now Stefan Berger
2021-11-30 16:06 ` [RFC 10/20] ima: Implement hierarchical processing of file accesses Stefan Berger
2021-11-30 16:06 ` [RFC 11/20] securityfs: Prefix global variables with securityfs_ Stefan Berger
2021-11-30 16:06 ` [RFC 12/20] securityfs: Pass static variables as parameters from top level functions Stefan Berger
2021-11-30 16:06 ` [RFC 13/20] securityfs: Build securityfs_ns for namespacing support Stefan Berger
2021-12-02 13:35   ` Christian Brauner
2021-12-02 13:47     ` Stefan Berger
2021-11-30 16:06 ` [RFC 14/20] ima: Move some IMA policy and filesystem related variables into ima_namespace Stefan Berger
2021-11-30 16:06 ` [RFC 15/20] capabilities: Introduce CAP_INTEGRITY_ADMIN Stefan Berger
2021-11-30 17:27   ` Casey Schaufler
2021-11-30 17:41     ` Stefan Berger
2021-11-30 17:50       ` Casey Schaufler
2021-11-30 16:06 ` [RFC 16/20] ima: Use ns_capable() for namespace policy access Stefan Berger
2021-11-30 16:06 ` [RFC 17/20] ima: Use integrity_admin_ns_capable() to check corresponding capability Stefan Berger
2021-12-01 16:58   ` James Bottomley
2021-12-01 17:35     ` Stefan Berger
2021-12-01 19:29       ` James Bottomley
2021-12-02  7:16         ` Denis Semakin
2021-12-02 12:33           ` James Bottomley
2021-12-02 17:54           ` Stefan Berger
2021-12-02 12:59         ` Christian Brauner
2021-12-02 13:01           ` Christian Brauner
2021-12-02 15:58             ` Casey Schaufler
2021-11-30 16:06 ` [RFC 18/20] userns: Introduce a refcount variable for calling early teardown function Stefan Berger
2021-11-30 16:06 ` [RFC 19/20] ima/userns: Define early teardown function for IMA namespace Stefan Berger
2021-11-30 16:06 ` [RFC 20/20] ima: Setup securityfs_ns " Stefan Berger
2021-12-01 17:56   ` James Bottomley
2021-12-01 18:11     ` Stefan Berger
2021-12-01 19:21       ` James Bottomley
2021-12-01 20:25         ` Stefan Berger
2021-12-01 21:11           ` James Bottomley
2021-12-01 21:34             ` Stefan Berger
2021-12-01 22:01               ` James Bottomley
2021-12-01 22:09                 ` Stefan Berger
2021-12-01 22:19                   ` James Bottomley
2021-12-02  0:02                     ` Stefan Berger
2021-12-02 13:18   ` Christian Brauner [this message]
2021-12-02 13:52     ` Stefan Berger

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